The present disclosure relates generally to bladed rotor manufacturing and, more particularly, to a method for manufacturing an integrally bladed rotor with hollow blades.
Integrally bladed rotors (IBRs), such as impellers, blisks, etc., employed in turbines and other machines are components of complex geometry. The design, construction and materials of IBRs often dictate operating limits for the turbines in which they are employed. Extensive efforts have been made over the years to develop new alloys, new fabrication techniques, and new component designs which permit operation of these rotors at higher operating temperatures and/or lead to lighter weight, longer lived components, with all their attendant advantages.
In order to reduce weight, the fan blades in some gas turbine engines are hollow. Each fan blade is made by combining two separate detail halves. Each half includes a plurality of cavities and ribs machined out to reduce the weight while forming a structurally sound internal configuration. One half forms the pressure side wall and the other half forms the suction side wall. When the detail halves are joined, the pressure side wall and the suction side wall are separated and supported by the ribs to form the hollow fan blade. The hollow fan blade is then subjected to forming operations at extremely high temperatures at which time it is given an airfoil shape and geometry. The side walls are contoured and curved to form the airfoil. The blades are then fixed to the hub or another element by laser welding or another joining technique.
Manufacturing a hollow-bladed IBR without subtractive manufacturing methods such as machining is currently not possible. While use of additive manufacturing in the formation of solid bladed IBR is trivial, there is currently no additive manufacturing method that would enable the precision formation of a hollow space in the center of a perfectly balanced blade, directly on the hub. Furthermore, thermal stresses generated in the bulky structure of massive components causes deformations of the individual layers formed during the manufacturing process. In the case of large massive components the deformation caused by thermal stress during melting and subsequent solidification of one layer of powder material can be so extensive as to negatively affect or even hindering the deposition of the subsequent powder layer, as the lower solidified and deformed layer obstructs the movement of the rack used to distribute the subsequent powder layer. Accordingly, the industry is receptive to new concepts that overcome these problems and which would enable production of an IBR with hollow blades.